1. Field of the Invention
The present invention relates to an apparatus and a method of inspecting solder printing and more particularly to an apparatus and a method of measuring the print deviation, the film thickness and the print pattern of the solder which has been supplied on the land pattern for attaching the components of a printed circuit board for surface mounting of the electronic components on a printed circuit board.
2. Description of Prior Art
The inspection apparatus for solder print according to a prior art is illustrated in FIG. 1.
In FIG. 1, numeral 1 designates a printed circuit board, numeral 2 a land pattern for mounting components, numeral 3 a paste-like solder supplied on the land pattern 2, numeral 5 a reference bore for positioning the printed circuit board 1, numeral 6 a positioning pin, numeral 7 a laser type displacement sensor, numeral 8 an orthogonal XY axes robot adapted to drive the laser type displacement sensor 7 in the X and Y directions, and numeral 9 a processing circuit adapted to process the signals from the laser type displacement sensor 7. The laser type displacement sensor 7 is fixedly mounted to the orthogonal XY axes robot 8.
Operation of the solder printing inspection apparatus as described above will next be explained.
The printed circuit diagram with the paste-like solder initially supplied to a part of the land pattern 2 is set on the jig 4. Then, the orthogonal XY axes robot 8 activates a scanning operation by the measuring point of the laser type displacement sensor 7 which then scans from the portion of the land pattern 2 to which the paste-like solder 3 has not been applied to the portion of the land pattern 2 to which the solder has been applied. The processing circuit 9 is adapted, upon reception of the signals from the laser type displacement sensor 7 which has thus scanned the land portion, to detect the height at the respective measuring points of the respective portions of the land pattern as described above. Since the positions of both portions having respectively been applied and not applied with the paste-like solder are detected in terms of height at the sampling points of the land pattern, the thickness of the film of the paste-like solder may be measured by searching the difference of height between the portions supplied with the solder and not applied with the same. According to the illustrated embodiment, since the surface of a part of the land pattern not supplied with the paste-like solder 3 is used as the reference surface for measuring the thickness of the film of the solder, an accurate film thickness measurement is made possible.
In this way, insertion of the positioning pin 6 of the jig 4 into the reference bore 5 of the printed circuit board 1 makes it possible to measure the film thickness of the paste-like solder 3.
The principle of measurement of the film thickness by the laser type displacement sensor 7 will next be described in connection with FIG. 2.
As shown in FIG. 2, the laser type displacement sensor 7 comprises an optical position sensing element 7a, a light reception lens 7b, a semiconductor laser 7c and a light projection lens 7d. The processing circuit 9 adapted to process the signals from the laser type displacement sensor 7 comprises an A/D converter 9a, a computing control section 9b and an input/output interface 9c. Measurement of displacement is carried out in such a way that a laser beam is irradiated on the surface of the portion of the land pattern to be measured and a portion of the diffused light emitted from the surface is then sensed by the optical position sensing element 7a. If the irradiated portion of the beam be displaced from the object A in FIG. 2 (the surface of the land pattern 2 serving as the reference) to the position B (the height of the paste-like solder 3 supplied on the land pattern 2), the beam spot on the optical position sensing element 7a will be moved in accordance with trigonometry. The amount of displacement is converted to an electric signal and the computing control section 9b computes the amount of displacement based on the electric signal. This amount of displacement or the thickness of the solder film may be obtained by subtracting the height B of the paste-like solder from the height A of the land pattern 2 serving as the reference for the laser type displacement sensor 7 in the following equation. EQU h=A-B
However, since the surface of the paste-like solder has a considerable undulation, the height displacement may be obtained by approximating the displacements at the respective sampling positions scanned by the laser type displacement sensor 7.
In the meantime as shown in FIGS. 3(a) and 4(a), the relationship between the scanning direction of the laser type displacement sensor 7 as moved by the orthogonal XY axes robot [i.e., X directions in FIGS. 3(a) and 4(a)] and the linear direction connecting the semiconductor laser 7c and the optical position sensing element 7a of the laser type displacement sensor 7 (referred hereinafter called as "light projection and light reception directions") is found both in the parallel scanning in which the light projection and light reception direction are in parallel with the scanning direction (X direction) and the orthogonal scanning in which the light projection and light reception direction are orthogonal to the scanning direction (X direction). In the case of the parallel scanning, the displacement of the steps (or edge portion) between the land pattern 2 and the paste-like solder 3 cannot be accurately measured as shown in FIG. 3(b) due to the influence by the light projection and the light reception regarding the laser beam. In order to cope with this problem, in the example shown in FIG. 1, the laser type displacement sensor 7 is fixed on the plane parallel to the printed circuit board so that the directions of light projection and light reception may be oriented in a Y scanning direction orthogonal to the X scanning direction (or the moving direction of the orthogonal XY axes robot 8) so as to allow an accurate measurement to be made when the laser type displacement sensor 7 is scanned in an X direction.
According to the solder printing inspection apparatus according to a prior art as explained above, since the laser type displacement sensor 7 is fixed to the orthogonal XY axes robot 8, scanning in one direction (X direction) in an orthogonal scanning operation is only available for measurement, so that accurate measurement of the film thickness and the print pattern cannot be expected. Besides, print deviation cannot be measured, so that such a measurement has to be done by way of a visual inspection.